Maps of the polarizations of high latitude Pi 2's

This manuscript presents a study of the polarizations of Pi 2's recorded by the magmetometer array of the University of Alberta. To simplify the interpretation, all the data are plotted in substorm‐centered coordinates (θ s ‐latitude, λ s ‐longitude). We have determined the center of the substorm current wedge (θ s = 0, λ s = 0) by using magnetometer data from midlatitude observatories to identify the ΔD crossover and magnetometer data from high latitude stations to identify the latitude of the onset of the substorm enhanced, westward electrojet. Within the region of the westward travelling surge, WTS, the polarizations in the horizontal H‐D plane are clockwise, CW (viewed downward), whereas equatorward of this region all polarizations are counterclockwise, CC, for all λ s . Far to the east and west of the WTS, the polarizations are CW, poleward of θ s = 0°, whereas poleward of the WTS the polarizations are CC. The orientations of the polarization ellipses suggest the presence of two distinct regions of field‐aligned current, FAC, associated with the Pi 2 oscillations. One region is centered near θ s = 0°, λ s = 5°E, and the other, possibly associated with the WTS, at θ s = 0°, λ = −10°E. Many of the features of the polarizations of the Pi 2's suggest that the overall morphology of the Pi 2 FAC, and ionospheric currents, are similar to that of substorm current systems, and that the elliptical polarizations observed on the ground are caused by azimuthal expansion of the FAC associated with the Pi 2. When these azimuthal motions occur, the latitudinally integrated FAC at a given longitude is phase‐shifted with respect to the latitudinally integrated ionospheric Hall current.